Chemically thickened polyester resin

ABSTRACT

THE VISCOSITY OF UNSATURATED POLYESTER RESINS FORMED BY MIXING THE CONDENSATION POLYMERS OF UNSATURATED DICARBOXYLIC ACIDS AND DIHYDRIC ALCOHOLS IN ETHYLENICALLY UNSATURATED COPOLYMERIZABLE MONOMERS MAY BE GREATLY INCREASED BY ADDING (1) A MIXTURE OF CALCIUM OXIDE AND EITHER CALCIUM HYDROXIDE OR MAGNESIUM OXIDE, AND (2) AN ORGANIC ACID SELECTED FROM THE GROUP CONSISTING OF BENZOIC ACID, CYCLOHEXANE CARBOXYLIC ACID, CINNAMIC ACID AND P-HYDROXYBENZOIC ACID TO THE UNSATURATED POLYESTER RESINS. THE VISCOSITY OF THE COMPOSITION IS INTIALLY LOW ENOUGH SO THAT FIBROUS REINFORCEMENTS CAN BE IMPREGNATED WITH THE RESIN COMPOSITION AND THE LOW VISCOSITY PERMITS THE RESIN TO WET THE FIBERS, THEREAFTER THE VISCOSITY OF THE RESIN INCREASES AND THE FIBROUS REINFORCED MASS LOSES ITS TACKINESS AND CAN BE EASILY STORED AND HANDED.

June 19, 1973 M. E. BAUM ETAL CHEMICALLY THICKENED POLYESTER RESIN Original Filed April l5, 1970 United States Patent Oiice 3,740,372 Patented June 19 1973 U.S. Cl. 260-40 R 1 Claim ABSTRACT OF THE DISCLOSURE The viscosity of unsaturated polyester resins formed by mixing the condensation polymers of unsaturated dicarboxylic acids and dihydric alcohols in ethylenically unsaturated copolymerizable monomers may be greatly increased by adding (l) a mixture of calcium oxide and either calcium hydroxide or magnesium oxide, and (2) an organic acid selected from the group consisting of benzoic acid, cyclohexane carboxylic acid, einnamic acid and p-hydroxybenzoic acid to the unsaturated polyester resins.

The viscosity of the composition is initially low enough so that brous reinforcements can be impregnated with the resin composition and the low viscosity permits the resin to wet the iibers, thereafter the viscosity of the resin increases and the brous reinforced mass loses its tackiness and can be easily stored and handled.

This is a division of application Ser. No. 28,600, filed Apr. 15, 1970, nOW Pat. N0. 3,637,911.

BACKGROUND OF THE INVENTION This invention relates in general to polyester resin compositions having a thickening agent therein.

United States Letters Patent No. 3,219,604, Polyester Resin Composition Modified by Monocarboxylic Acid and Metallic Bridging Agent, describes that polyester resin compositions can be thickened by heating the resins with either Imagnesium oxide, aluminum oxide or calcium oxide and an aliphatic monocarboxylic acid having from 6 to 24 or more carbon atoms in the chain to a temperature of 140 to 250 F. for a period of from 5 minutes to 40 hours so long as a large quantity of inhibitor is present to prevent polymerization. An inherent tendency, of course, is for the polymer resin to partially cure to a gel state at elevated temperatures.

U.S. Pat. No. 3,465,061, Unsaturated Polyester Resin Compositions Having a Thickening Agent Therein, describes a product Iwhich is initially thin but within a day becomes thick, without the application of heat, formed by adding to an unsaturated polyester resin an oxide of a Group II-A metal and an anhydride of a cyclic hydrocarbon. According to Pat. No. 3,465,061, maleic anhydride and phthalic acid are not particularly effective for thickening the polyester resin; the anhydrides of cyclic hydrocarbons must be used.

There are some other thickening systems that do not require the application of heat to produce the thickening eiiect. U.S. Pat. 3,431,320, Polyester Resin Composition Having a Thickening Agent Therein describes that the chemical thickening of polyester resins by the addition oi Ca(OI-I)2 or MgO can be greatly enhanced by the addition of CaO. According to Pat. No. 3,431,320, despite a rapid high viscosity build-up, the pot life of the resin can be extended. This finding enabled sheets to be made, for example, such as tbrous mats impregnated with the polyester resin wherein the resin thickened to yield sheets which were capable of being stacked, with release agents therebetween, for a period of time without the sheets flowing, i.e., changing dimensions an undesirable amount or the glass iibers separating from the resin.

SUMMARY oF THE INVENTION It has now been discovered that the thickening effect described in U.S. Pat. No. 3,431,320 can be greatly accelerated by the addition of certain monocarboxylic acids, each having a six carbon ring member in its structure, to the unsaturated polyester resin containing a mixture of calcium hydroxide or magnesium oxide and calcium oxide. The thickening is accelerated Without the application of heat to the composition and, therefore, large amounts of polymerization inhibitors do not have to be added to the composition to prevent premature curing to a gelation state.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates generally in the block diagram the resinous composition.

FIG. 2 illustrates a layer made in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the invention a resin composition which greatly increases in viscosity is produced from an unsaturated polyester resin which includes an unsaturated polyester formed by condensing at least one dicarboxylic acid containing a,ethylenic unsaturation with a dihydric alcohol and an a,ethylenically unsaturated copolymerizable monomer, preferably a styrene or vinyl-type monomer, by the addition to the resin of a thickening agent in an amount sufficient to increase the viscosity of the composition after a period of time, said thickening agent consisting of a mixture of (l) calcium oxide CaO and (2) either calcium hydroxide Ca(OH)2 or magnesium oxide MgO and an effective amount of a monocarboxylic acid having a six carbon ring member in its structure and selected from the group consisting of:

benzole acid (l) and p-hydroxybenzoic acid cyclohexane carboxylic acid einnamlc acid The amount of the calcium oxide, calcium hydroxide and magnesium oxide added to the unsaturated polyester resin may vary somewhat depending upon the amount of viscosity build-up desired. It has been found, however, that at least 0.5% by weight of calcium oxide based on the total weight of the polyester resin must be present. It has also been found that the magnesium oxide or calciurn hydroxide must be present in an amount by weight of at least 0.5% based on the weight of the polyester resin. Larger amounts of calcium oxide, calcium hydroxide or magnesium oxide may be used; the large amounts act more as llers and are unnecessary to produce the rapid chemical thickening when the organic accelerators are used in accordance with this invention. Amounts of the monocarboxylic acids as low as 0.25% by Weight based on the weight of the polyester resin are effective in producing the thickening accelerating eifect of the invention. Generally, amounts of from 0.5% to 2.0% by weight of the monocarboxylic acids based on the weight of the polyester resins are used in the practice of the invention. Larger amounts of the monocarboxylic acids also act as fillers and do not justify, on the basis of results, the expense involved.

Unsaturated polyester resins are commercially available from a number of sources. By unsaturated polyester resin is meant a mixture of the polyester and a copolymer-izable monomer.

The unsaturated polyester is formed by polyesterifying dicarboxylic acids with dihydric alcohols. Approximately equimolar proportions of the dicarboxylic acids and dihydric alcohols are used. To provide unsaturation with-in the polyester, at least a portion of the dicarboxylic acids contain ethylenic unsaturation. Maleic and fumarie acids are common examples of ethylenically unsaturated dicarboxylic acids. Mixed with these acids may be dicarboxylic acids that are saturated normal aliphatic acids such as adipic acid, succinic acid, or the like, or that are aromatic dicarboxylic acids such as phthalic acid, isophthalic acid or the like as well as halogenated derivatives of such aromatic acids, for instance, tetrachlorophthalic anhydride.

Illustrative of the dihydric alcohols used for the production of polyesters are ethylene glycol, propylene glycol, 1,2-butanediol, i1,3butanediol, lA-butanediol, diethylene glycol, polypropylene glycol, 2,2-dimethyl-l,3- propanediol, 1,4-cyclohexane dimethanol and adducts or reaction products of alkylene oxides with 2,2bis(4hy droxy phenylene) propane (bis-phenol A).

To produce the polyester resin, the unsaturated polyester is dissolved in a a,;8-ethylenically unsaturated monomer. The amount of monomer used generally is about 20-70% (and preferably Sil-60%) by weight of the total polyester resin. If the percentage of monomer is too low the viscosity of the nal resin will be initially too high for good wetting of the glass bers and the amount of cross-linking of the iinal product will be small so that characteristics such as dellection temperature and tensile strength are not that which are normally desired. On the other hand, too much monomer may cause an undesirable shrinkage during curing and an undesirable exotherm during curing. Preferably 30-60% of monomer by weight is used. The unsaturated polyester resin (polyester and monomer) is then cured by initiating a free radical polymerization between the ethylenically unsaturated monomer and the unsaturated polyester at the a,ethylenic double bonds in the polyester. This copolymerization is commonly initiated by addition of a free radical generating catalyst followed by heating. The polyester and monomer compositions of the polyester resin copolymerize to forma cross-linked thermoset resin.

Illustrative of the copolymerizable ethylenically unsaturated monomers are styrene, u-methylstyrene, chlorostyrene, vinyl toluene, divinyl benzene, diallylphthalate, methyl methacrylate and the like.

Examples of the free radical generating catalysts are peroxide catalysts such as benzoyl peroxide, methylethyl ketone peroxide, cumene hydroperoxide, and the like. Other free radical generating catalysts may also be used as, for example: 2,2'-azobisisobutyronitrile. Preferably the catalyst system selected is one which is inactive at room temperature since the invention contemplates a desired use of a thickened, yet unpolymerized resin which retains the exibility of an uncured resin. In accordance with this invention, the catalyst is generally added after the thickeners have been added to avoid any premature gelation which may result from the heat of mixing.

The compositions of this invention can be readily made from commercially available materials. As an illustration, to obtain 100 parts by weight of the polyester resin, 30-80 parts of an unsaturated polyester made from the condensation reaction of approximately equimolar proportions of the dihydric and dicarboxylic acids are dissolved in, by diiference, 2.0-70, and preferably, 30-60, parts of one of the a8ethylenically unsaturated monomers, i.e., the resin is the polyester dissolved in the monomer. To the parts by weight of the resin are added a mixture of at least 0.5 part by weight of calcium oxide and 0.5 part by weight of either calcium hydroxide or magnesium oxide and an elfective amount of a monocarboxylic acid selected from the group consisting of benzoic acid, cyclohexane carboxylic acid, cinnamic acid and p-hydroxybenzoic acid. The mass lis mixed with a conventional mixer, for example a Cowles mixer, until the mass is thoroughly mixed, usually a matter of minutes. Then the catalyst is added and mixed into the mass.

Conventional fillers, pigments and mold release agents can be mixed into the polyester resin at anytime during the production of the chemically thickened resin. Generally, however, they are added prior to the addition of the thickener.

in use a layer of the composition to which the thickener, filler, pigment and catalyst have been added is poured onto a lm of polyethylene which is moving past the pouring point. A layer of chopped glass is then dropped onto the moving resin-coated film, across the width of the lilm. Onto another sheet of polyethylene film is poured the resin composition and the sheet ipped over; the resin composition is sufficiently thick to prevent the resin from dripping from the polyethylene iilm. The second sheet is thus applied to the irst sheet in such a manner that the surface of the chopped glass-resin system is in contact with the resin composition surface of the other sheet so as to sandwich the layer ofchopped glass between the two layers of resin.

The Weight of the glass in the mass of resin and glass ber is chosen according to the properties desired of the polyester after it has been cured. As the weight of glass is increased the strength of the cured polyester increases. The surface appearance of the cured polyester, however, suffers as the weight of glass in the cured polyester increases. Generally, the glass makes up 15-30% of the mass of resin and glass bers. The sheets are then passed between two pressure rollers with the polyethylene film in contact with the rollers to squeeze the resin layer into the liber layer to enable the resin to penetrate the chopped glass layer and wet the glass bers. The viscosity of the resin is initially suiciently low to wet the glass ibers and to allow the resin layers to blend together. However, the viscosity of the resin composition rapidly increases and the mass of resin and glass bers loses its tackiness. Accordingly, workmen can remove the polyethylene film and stack the layers of composition and ber mass after a period of only one to two days. The individual layers may be removed from the stack at will and placed in a mold for molding in accordance With conventional molding techniques.

The invention will be further understood by referring to the block diagram of FIG. 1 and the following examples.

EXAMPLE 1 To illustrate the practice of this invention aliquots were taken from a commercially available unsaturated polyester resin sold under the trademark KOPLAC Grade 2000 (made by the condensation of 1.0 mole each of maleic anhydride and phthalic anhydride with approximately 2.0 mole of propylene glycol). The resin was analyzed to contain 40% styrene and 60% polyester and to have an acid number of about 15.8. To 100 parts of each aliquot was added 3.2 parts of calcium oxide and 2.8 parts of calcium hydroxide and, except for aliquot (l), there was added 0.7 part of a monocarboxylic acid in accordance with the invention. The viscosities in each case through this specification were measured with a Brookeld Syncrolectric Viscometer (Model LVT up to 2 million centipose and Model HBT up to 64 million centipoise). The results are tabulated below:

From the foregoing it is evident that the accelerating effect of the invention can be controlled by varying the TABLE I Viscosity in cps. 3 after- Aliquot Acid 1 day 2 days 2 Weeks 3 Weeks 2 months 4 months (1) Non@ 15 85 190 360 (2) Benzoie- 2, 85o 3, 850 4, 400 5,400 6, 700 15, 700 (3)- Cinnam1c- 183 690 500 380 600 1,800 4) p-Hydroxybenzo 76 123 215 210 345 470 Cyclohexane carboxylic 3, 400 5, 000 5, 700 5, 100 10,200 64, 000

From the foregoing it is evident that the benozic acid and cyclohexane carboxylic acid are the most effective in promoting greater thickening. It will be noted, however, that with the calcium hydroxide/ calcium oxide thickening agents previously known, all of the monocarboxylic acids set out in the table were effective in accelerating the thickening.

EXAMPLE II To five aliquots of another commercially available unsaturated polyester resin, KOPLAC Grade 6101 (made by condensing 1.0 mole isophthalic acid and 1.4 mole maleic anhydride with 0.8 mole dipropylene glycol and about 1.7 mole of propylene glycol), analyzed as containing 70% polyester and 30% styrene, was added enough monomeric styrene to dilute the resin to a 60/40, polyester/ styrene, ratio. The acid number of these diluted aliquots was analyzed to be 13.2. To 100 parts of each of the diluted aliquots was added 3.2 parts calcium oxide and 2.9 parts calcium hydroxide and, except for aliquot (l), the specified parts of benzoic acid as set out below:

amounts of calcium oxide and calcium hydroxide or magnesium oxide added to the unsaturated polyester resin containing an effective amount of the monocarboxylic acid. Generally, however, it is not necessary for the total amount of calcium oxide and calcium hydroxide or magnesium oxide present in the thickened composition to exceed 6% by weight to achieve a sufficient rapid viscosity thickening to produce the moldable layers of the invention.

A fiexible layer, suitable for matched-die molding was produced from the composition of the invention by adding to 100 parts of a seventh aliquot of the KOPLAC Grade 6101 resin of Example III a mixture of 3.2 parts of calcium oxide and 2.9 parts of calcium hydroxide and 0.75 parts of benzoic acid. After thoroughly mixing the aliquot, the resin was poured onto a moving sheet of polyethylene film having a width of 24 inches. A layer of strands of one inch length of OwensJCorning Type 415 fiber glass were dropped onto the moving resincoated film, across the width of the film. The resin was also poured onto a second film of polyethylene and the TABLE II Viscosity in cps. 10a after- 1 day 7 days 2 weeks 1 month 2 months 3 months 4 months 44o 700 1, 040 1, 150 1, soo 2, 40o 3, 450 1, 460 3, 200 700 5, 600 5, 950 8, 300 8, 650 1, 600 4, 000 6, 200 6, 000 10, 400 12, 700 4, 000 10, 600 13, 400 19, 000 21, 000 29, 500 31, 000 3, 100 13, 000 14, 400 16, 000 29, 000 29, 800 41, 500

Table II illustrates the accelerating effect of benzoic acid on the thickening effect of the previously known calcium hydroxide/ calcium oxide thickening agents. It is evident from the table that the accelerated effect increases as the concentration of acid in the unsaturated polyester resin increases. Similar results were obtained with cyclohexane carboxyl acid, cinnamic acid and p-hydroxybenzoic acid. It will be noted that the concentration of monocarboxylic acid used will depend on the accelerating effect desired. Generally, however, sufficient thickening for producing a moldable and stackable layer of the invention is obtained with the amounts of acid set out in Table II. Larger amounts of the monocarboxylic acids tend to act as filler and are not justified from a cost standpoint.

IEXAMPLE III To 100 parts of each six aliquots of the commercially available KOPLAC Grade 6101 unsaturated polyester resin described in Example II (70/30 polyester/styrene ratio and having an acid number of 15.4) were added, as set out below, the specified parts of calcium oxide, calcium hydroxide and, except for aliquots (1) and (2), cyclohexane carboxylic acid.

resin-coated sheet flipped over. The resin is sufficiently thick to prevent the resin from dripping off of the film.

The amount of chopped glass dropped onto the resincoated film was approximately 20% by weight (based on the final glass-resin system). The resin composition face of the second film was brought into contact with the glass-resin composition face of the first film and passed between pressure rollers with the polyethylene film in contact with the rollers so that the layers were squeezed to cause the resin to penetrate the layer of chopped glass and Wet the glass fibers.

Several days later the layer of resin and glass was placed in a matched-die mold and heated to a temperature of 280-300 F. for approximately three minutes. Removed from the mold the cured article had a smooth surface appearance and good hardness.

A layer of the type described above is illustrated in FIG. II. The layer is fiexible, moldable, storable and nontacky Within a period of time after formation of the layer.

Thus, the chemically thickened resins of the invention have an initial viscosity low enough to insure proper wetting of glass fibers coated with the resins. The viscosities TABLE III Parts cyclohexane Parts Parts Viscosity in cps.X10-3 carboxylic calcium calcium acid oxide hydroxide 1 day 7 days 2 weeks 1 month 2 months (l) 1. 0 1.00 185 50o 920 1,500 2, 35o 1. 0 1. 50 140 380 800 1, 200 2, 000 (3) 0. 5 1. 0 1. 0 1. 1 480 1, 020 1, 760 4,000 0. 5 1. 0 1. 50 215 800 1, 400 2, 700 5, 400 0. 5 3. 0 1. 0 54.0 9, 000 10, 700 12, 800 14, 100 0.5 3. 0 1. 25 2, 200 13, 000 14, 700 17, 600 19, 800

of the resin greatly increase within a spaced period of time thereafter, whereby mats of the coated glass and bers lose their tackincss and can be easily handled and stored.

What is claimed is: f 1. A layer that is curable under the inuence of heat to a thermoset reinforced plastic comprising per 100% by Weight of said layer of (a) from 70 to 85% by Weight of a chemically thickened unsaturated polyester resin and (b) from 15 to 30% by Weight of glass bers; said resin being comprised of (i) from 80 to 30% by weight of an unsaturated polyester formed by condensing at least one dicarboxylic acid containing aethylenic unsaturation with a dihydric alcohol,

(ii) from 20 to 70% by weight of an a,-ethyleni cally unsaturated copolymerizable monomer, and

(iii) a thickening agent in an amount suicient to increase the viscosity of the composition after a period of time, said thickening agent consisting of (a) at least 0.5% by Weight based upon the Weight of said unsaturated polyester resin of a mixture of calcium oxide and at least 0.5% by Weight of a compound selected from the class consisting of calcium hydroxide and magnesium oxide, and (b) a monocarboxylic acid selected from the class consisting of benzoic acid, cyclohexane carboxylic acid, cinnamic acid and phydroxy-benzoic acid in an amount of from 0.25% to 2.0% based upon the Weight of said unsatuarted polyester resin, and

(iv) a free-radical generating catalyst;

said layer being flexible, moldable, storable, non-tacky Within a period of time after formation of the layer and resistant to migration of the glass fibers within said layer.

References Cited UNITED STATES PATENTS 3,431,320 3/1969 Baum et al. 260-865 3,390,205 6/1968 Schnell et al. 260-863 X 3,557,042 1/1971 Dalhuisen 260-865 X 3,219,604 11/1965 Fischer 260-863 X MORRIS LIEBMAN, Primary Examiner S. M. PERSON, Assistant Examiner US. C1. X.R. 260--861, 863 

